Wireless communication devices often require multi-band antennas for transmitting and receiving radio communication signals often called Radio Frequency (RF) signals. For example, network operators provide services on a GSM system in a 900 MHz frequency band typically used in Asia also use a DCS system in a 1800 MHz frequency band typically used in Europe. Accordingly, GSM wireless communication devices, such as cellular radio telephones, should have dual band antennas to be able to effectively communicate at least at both of these frequencies. Also, in certain countries service providers operate on 850 MHz or 1900 MHz frequency bands. Accordingly, GSM wireless communication devices, such as cellular radio telephones, should have multi band antennas to be able to effectively communicate on more than one of these frequency bands.
Current consumer requirements are for compact wireless communication devices that typically have an internal antenna radiator structure instead of an antenna stub that is visible to the user. There has also been a recent trend towards thin form factor cellular telephones. These thin form factor cellular telephones require a miniaturized antenna radiator structure comprising an antenna radiator structure coupled to a ground plane, the ground planes being typically formed on or in a circuit board of the telephone. Further, these internal antenna radiator structures (patch antennas), such as a Planar Inverted F Antenna (PIFA) or Planar Inverted L Antenna (PILA), that use a radiator element in the form of a micro-strip internal patch antenna, are considered advantageous in several ways because of their compact lightweight structure, which is relatively easy to fabricate and produce with precise printed circuit techniques capable of integration on printed circuit boards.
Internal antenna radiator structures are typically installed inside a cellular phone where congested conductive and “lossy” components are placed nearby. The internal antenna radiator structures must therefore preferably be able to cover multiple frequency bands to, for instance, accommodate the 850 MHz, 900 MHz, 1800 MHz, 1900 MHz bands whilst not being the deciding factor that limits the thin form factor.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.